For the most part, I dont believe you can sex BRs by feathers. I just answered this question several times on the board. There are three traits, that taken together, will tell you the sex of BRs about 90% of the time.
Down color very black= female..... silvery/frosty = male
Headspot defined/smallish...female......large, splotchy, with frost around back of head= male
Leg color very dark wash down front=female..little or none=male
On occasion I see a lighter colored female or a darker color male or one that just looks in-between and cant make a decision.